As a process of producing lysihopril (VIII), there are known a process of reacting .beta.-phenylpropionaldehyde and N.sup.6 -tert-butoxycarbonyl-L-lysine (VII) with potassium cyanide (Strecker reaction) to form a compound shown by formula (X) below, successively treating the compound (X) with hydrogen chloride/methanol and an acid ion exchange resin to form a diester derivative shown by formula (XI) shown below, and hydrolyzing diester with alkali (VI) as shown in the following reaction formula (JP-A-58-113158) (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). ##STR2## Also known is a process of reacting the N-carboxy anhydride of N.sup.6 -trifluoroacetyl-L-lysine and L-proline to provide N.sup.6 -trifluoroacetyl-L-lysyl-L-proline shown by formula (XII) below, reductively alkylating the proline derivative (XII) with ethyl a-oxo-.gamma.-phenylbutyrate (XIII) to form N.sup.6 -(1-ethoxycarbonyl-3-phenylpropyl)-L-lysyl-L-proline shown by formula (XIV) below, and then hyroxylzing the proline derivative (XIV) with alkali as shown by the following reaction formula (JP-A-61-36297). ##STR3##
However, the materials or pigments used in the aforesaid processes except .gamma.-phenylpropionaldehyde, L-proline, and potassium cyanide have the following disadvantages. That is, they have complicated structures, can be not always easily available, are expensive and require considerable many steps for the synthesis thereof. Also, for obtaining an isomer having an absolute configuration inevitable for that (S,S,S) lysinopril shows activity as an angiotensine conversion enzyme inhibitor (ACEI), it is desirable to separate starting materials, inclusive of intermediates so as to obtain the final product in high purity since the starting material are expensive and may be easily separated through an optical resolution. Thus, the aforesaid processes have difficulties in economy and operability as a practical production process of lysinopril.
The inventors previously discovered a process of efficiently producing .alpha.-(1-carboxyethyl)amino-.gamma.-phenyl-butyric acid ethyl esters which are very useful as the intermediates for producing many ACEIs by using Strecker reaction using inexpensive starting materials as described in Japanese Patent Application No. 62-204860.